The present invention relates to a copper base spring material for use in electrical contacts that has high strength and toughness, as well as good adhesion of solder and which has reduced anisotropy in characteristics in that its characteristics do not differ greatly in two directions, i.e., the working direction and the direction perpendicular to it.
Copper base alloys containing 2-5 percent by weight of Ti (all percents noted hereinafter are on a weight basis) are precipitation hardening type copper alloys that have strength comparable to beryllium copper and have conventionally been used as contact materials, or spring materials for use in electrical contact members such as connectors and switches that require high strength and toughness.
Typical conventional electrical contact arrangements are shown in FIGS. 1-4.
The demand for smaller and lighter device parts has increased constantly these days and to meet this need, a tendency toward decreasing the wall thickness of parts while increasing their strength is inevitable. If the amount of working increases as in the case of rolled or drawn materials, their mechanical characteristics will become greatly different in two directions, i.e., the working direction and the direction perpendicular to it. The anisotropy in characteristics is fatal to spring materials, particularly, to the threshold value of springs or resistance to cyclic bending. If inhomogeneity in materials characteristics occurs in electrical contacts that need to be bent in complex shapes for their fabrication, torsion will occur after working or their dimensional precision is impaired to such an extent that the intended bending becomes practically impossible.
The anisotropy in characteristics is particularly noticeable in the prior art Cu-Ti alloy described above and several disadvantages will occur. First, the alloys cannot be worked by the necessary great amount. Secondly, the working process requires an extra step of heat treatment under sufficiently elevated temperatures to eliminate the anisotropy. However, not only does this lead to a complex and costly working process but also the high temperatures employed will inevitably cause grain growth, embrittlement and oxidation.